1. Field of the Invention
The invention relates to a method for torque control of an internal combustion engine and to an internal combustion engine employing the method.
2. Description of the Related Art
Methods for torque control of internal combustion engines are known in the prior art. A method is known from German disclosure document DE 10 2010 051 370 A1, wherein with the assistance of a pressure sensor an internal cylinder pressure is determined in a guide cylinder. From the speed information a first torque is determined for each cylinder of the internal combustion engine, whereas a second torque is determined from the internal cylinder pressure which was recorded for the guide cylinder. Based on the respective first torque and a second torque an indexed torque is determined for each cylinder. A preferred embodiment provides that the second torque which is determined for the guide cylinder is used for quality assessment of the determined first torques. The reference determines a functional efficiency of the pressure detector via the first torques and provides a simple diagnostic option. The amount of fuel injected for the individual cylinders depends upon the indexed torque of each cylinder which is determined with the assistance of the respective first torque or respectively the second torque. With this method, injection control and torque control are tightly interrelated and in particular the second torque that was determined for the guide cylinder is regularly compared and/or balanced with the first torques which were determined based on the speed information. This renders the method unduly complicated. Furthermore, one cannot assume that the second torque that was determined for the guide cylinder on the basis of the pressure measurement is characteristic for the entire internal combustion engine.
An underlying problem is that injectors for injecting fuel into cylinders of an internal combustion engine, for identical control, in particular in energizing, display manufacturing related variances in their opening behavior. If the injectors of the internal combustion engine are controlled with identical energizing parameters, in particular with an identical energizing duration, they nevertheless inject different fuel amounts into the individual cylinders. With low injection amounts the variance is so large that some injectors inject fuel into the cylinders that are assigned to them, whereas others do not open. Pre-injection and after-injection are therefore not realizable if the injectors vary strongly. Moreover, the individual cylinder pressure values differ greatly among each other and the cylinders differ greatly from one another in regard to the torques produced by them. If therefore, the injectors are not adjusted or respectively equalized in regard to their injection behavior, a pressure sensor has to be assigned to each cylinder for torque control, because no single cylinder pressure can be characteristic for the entire combustion engine. Overall it is therefore desirable to reliably reduce the variance in the opening behavior of the injectors in operation of the internal combustion engine.